This invention relates to the recovery of precious metals using leaching, in particular the leaching of precious metals, especially gold (Au), silver (Ag) and/or platinum group metals (PGMs), from ores, concentrates or tailings.
Current practice involves the use of cyanide (CN—) to leach gold from ores. While cyanide is (mostly) a very effective leach reagent for gold, it is also a very toxic chemical and a serious ecological threat. The negative environmental impact of cyanide spillages at several gold operations has raised concerns in recent years over the continued use of cyanide in gold operations.
Pressure to develop alternative processing routes for gold has led to investigations into a number of reagents. For various reasons, commercial application of these reagents to the gold industry has been slow. High reagent consumption in thiourea and thiosulphate leaching, the suspected carcinogenic properties of thiourea and the highly specialised equipment required to withstand corrosion in chloride leaching are just some of the reasons for the limited application of cyanide alternatives to gold leaching. These are discussed in detail in “Alternatives to cyanide in the gold mining industry: what prospects for the future”, Hilson and Monhemius, Journal of Cleaner Production, 14, 1158-1167, 2006.
It is an object of this invention to provide a new process for the leaching of gold (Au), silver (Ag) and platinum group metal (PGM) ores, concentrates and tailings, which addresses the problems discussed above.